Theories about the Origin of Living Beings
1. Controversy between biogenists and abiogenistas.
The first theory about the origin of life is that of the spontaneous generation that states that: life could arise from mud, rotting matter, sea water, dew and garbage. This theory managed to stand for many years, as it was supported by Aristotle and the Church, the latter with a variant called vitalism that held: it is necessary the presence of a vital force, a divine breath or a spirit, capable of giving life to inert matter. Some time later, the unbelieving scientists try to refute the theory of spontaneous generation and Francisco Redi accomplishes this by using pieces of meat, but shortly thereafter, Needham, boiling nutritious broths for a short time, tries again to verify the theory of spontaneous generation and with his experiment succeeds. But in the same century Spallanzani refuted Needham’s experiment by boiling the broths longer, however this was not accepted by the church because it considered that the broths were excessively boiled.
Concerned about trying to solve the problem, the French academy of sciences calls for a contest offering a prize to the one who refutes or who really proves the theory of spontaneous generation. And Louis Pasteur manages to refute it with his experiment that consisted of boiling (even killing the microorganisms) the broth contained in long-necked flasks in the form of S folded horizontally. And as time passed and the flasks were not infested with microorganisms, it was found that they were in the air when they found the necks of the flasks full of microbes.
2. Theory of the chemical origin of life formulated by Oparin-Haldane.
About 3500 million years ago, the physical and chemical conditions of the Earth were very different from the current ones: the atmosphere lacked free oxygen, so it was strongly reducing, it was composed of hydrogen, methane, ammonia and water vapor. There was a moderate temperature with very hot areas in the vicinity of volcanoes and thermal springs; the oceans and lakes had a basic pH; In addition, there were high-energy radiations from outer space. Under these conditions, some chemical compounds of simple molecules were combined to give rise to more complex ones. This process is known as chemical evolution. The chemical reactions proposed by Oparín to give rise to the biomolecules probably occurred and they mixed the organic products of those reactions. The sea, the shallow lagoons and the puddles became primitive broths where the molecules collided, reacted and grouped together giving rise to new molecules and molecular aggregates of different size and complexity. The forces of intermolecular attraction were very important in these reactions.
3. Characteristics of the primitive earth and synthesis of organic molecules.
The Earth was acquiring its form through millions of years. The bark and primitive atmosphere were formed of light materials located on the outside. Volcanic eruptions poured lava from the warm regions of the interior, increasing the material of the crust. The steam from the volcanoes condensed and fell in the form of rain to form the oceans.
The atmosphere of the Primitive Earth probably consisted of: ammonia and methane or nitrogen and Carbon Dioxide and with small amounts of hydrogen and water vapor. The gases of the primitive atmosphere, probably, contained the elements that we find in living organisms: carbon, hydrogen, oxygen and nitrogen, so possibly, from these gases formed the main organic molecules.
Origin of prokaryotes.
Precellular systems: The precellular systems according to Oparín are the Coacervados. A coacervate is a group of microscopic droplets formed by attraction between molecules. Coacervates can be formed from a mixture of proteins and sugar in water.
First Living Beings Because the procaryotic cells are the simplest, the most primitive cells on Earth must have been simple prokaryotic cells.
It is very difficult to pinpoint exactly when they first appeared or to know the nature of the first types of organisms. However, some prokaryotes seem to have appeared first than others.
Origin of eukaryotes.
The main current theory about the origin of eukaryotes is the endosymbiotic theory of Margulis:
It is a way to explain the origin of eukaryotes. Margulis, suggests that chloroplasts, mitochondria and flagella are cellular c-rganelos that derived from free-living prokaryotes and that by a process of endosymbiosis were part of a single cell. To explain the above, he proposes that a great variety of prokaryotes must have existed on the primitive earth, some aerobic and other photoautotrophic, as well as various forms of them: amiboideos, spherical, spiked, etc., and that some amiboide prokaryote swallowed another of aerobic respiration but without digesting it, resulting in a cell with mitochondria, chloroplasts or primary flagella